Doctors’ stethoscopes are contaminated with bacteria that can easily be transferred from one patient to another, a new study has found.

Researchers cultured bacteria from the fingertips, palms and stethoscopes of three doctors who had done standard physical examinations on 83 patients at a Swiss hospital. They tested for the presence of viable bacterial cells, looking specifically for the potentially deadly methicillin-resistant Staphylococcus aureus, or MRSA. The study appears in the March issue of the Mayo Clinic Proceedings. Fingertips on the doctors’ dominant hands were the most contaminated, but the part of the stethoscope that touches the patients’ skin held more than twice as much bacteria as the physicians’ palms. The stethoscopes were more contaminated with MRSA than some parts of the palms, but not others. The authors acknowledge that the study was small and may not be applicable to other health care sites. Except for MRSA, they did not distinguish harmful from harmless bacteria.